Abstract
The Transmission Assessment Survey (TAS) is a decision-making tool to determine when transmission of lymphatic filariasis is presumed to have reached a level low enough that it cannot be sustained even in the absence of mass drug administration. The survey is applied over geographic areas, called evaluation units (EUs); existing World Health Organization guidelines limit EU size to a population of no more than 2 million people. In 2015, TASs were conducted in 14 small EUs in Haiti. Simulations, using the observed TAS results, were performed to understand the potential programmatic impact had Haiti chosen to form larger EUs. Nine "combination-EUs" were formed by grouping adjacent EUs, and bootstrapping was used to simulate the expected TAS results. When the combination-EUs were comprised of at least one "passing" and one "failing" EU, the majority of these combination-EU would pass the TAS 79% - 100% of the time. Even in the case when both component EUs had failed, the combination-EU was expected to "pass" 11% of the time. Simulations of mini-TAS, a strategy with smaller power and hence smaller sample size than TAS, resulted in more conservative "passing" and "failing" when implemented in original EUs. Our results demonstrate the high potential for misclassification when the average prevalence of lymphatic filariasis in the combined areas differs with regards to the TAS threshold. Of particular concern is the risk of "passing" larger EUs that include focal areas where prevalence is high enough to be potentially self-sustaining. Our results reaffirm the approach that Haiti took in forming smaller EUs. Where baseline or monitoring data show a high or heterogeneous prevalence, programs should leverage alternative strategies like mini-TAS in smaller EUs, or consider gathering additional data through spot check sites to advise EU formation.
Highlights
Lymphatic filariasis (LF) is a vector-borne disease caused by nematodes, or roundworms, that reside in lymphatic vessels and can lead to debilitating disability, as well as stigma, psychological problems, and lowered quality of life [1,2]
Lymphatic filariasis is a disease caused by roundworms that may lead to disability, psychological problems, stigma, and lowered quality of life
One of the key strategies to control and eliminate lymphatic filariasis is mass drug administration (MDA), or repeated treatment of all at-risk people living in affected areas with an annual dose of medicine
Summary
Lymphatic filariasis (LF) is a vector-borne disease caused by nematodes, or roundworms, that reside in lymphatic vessels and can lead to debilitating disability, as well as stigma, psychological problems, and lowered quality of life [1,2]. There are costs associated with implementing MDA; to maximize the use of scarce public health resources, it is important for programs to know when MDA can be stopped with minimal risk of recrudescence. A 2011 study of communes in Haiti that received MDA found the cost of MDA distribution in the first year of the national strategic plan in just nine out of 55 communes to be $264,970. Extending this cost to all of the communes in program amounts to about $1,214,102 for just one year, not including the cost of albendazole [5]. The work is made available under the Creative Commons CC0 public domain dedication
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